Electric power converter

ABSTRACT

A processor unit in an electric power converter executes detection of an overheating predicted state that is a stage prior to overheating of the IGBTs, a short circuit predicted state that is a stage prior to a short circuit in the arms, and a voltage drop predicted state that is a stage prior to a drop in a control voltage to be supplied to a driver circuit. When none of these predicted states is detected, a determination that an abnormality is not caused in the power module based on a latch signal is made by the processor unit. When an overheating predicted state is detected, the processor unit lowers the duty ratio of a motor control signal. When a short circuit predicted state is detected, the processor unit prolongs the dead time in which the upper IGBTs and the lower IGBTs are both maintained in the off-state.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2013-200348 filed onSep. 26, 2013 including the specification, drawings and abstract, isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an electric power converter.

2. Description of the Related Art

There is a conventional electric power converter that includes: a powermodule including a plurality of power semiconductor devices such asinsulated gate bipolar transistors (IGBTs); and a processor unit thatcontrols the operation of the power module. Such an electric powerconverter is mounted in a vehicle such as an electric vehicle or ahybrid vehicle. The power module of the electric power converterconverts direct-current power supplied from a driving electric powersource into alternating-current power, and then supplies thealternating-current power to a motor (load).

Specifically, the power module includes: an inverter circuit in whichmultiple arms, each including power semiconductor devices connected inseries, are connected in parallel; and a driver circuit that outputs, toeach power semiconductor device, a drive signal (gate on-off signal),which is obtained by amplifying a control signal output from theprocessor unit based on a control voltage supplied from the outside.Each power semiconductor device is turned on or off based on the drivesignal, and thus alternating-current power is supplied from the invertercircuit to the motor.

Recently, some electric power converters include, as a power module, aso-called intelligent power module (IPM) including an abnormalitydetection circuit that detects abnormalities such as overheating ofpower semiconductor devices, a short circuit in arms, and a drop in thecontrol voltage supplied (applied) to a driver circuit (see, forexample, Japanese Patent Application Publication No. 7-274485 (JP7-274485 A)). When some sort of abnormality is detected by theabnormality detection circuit of the power module, a processor unitexecutes a failsafe process such as a process of stopping a motor.

Generally, such a power module is configured to output, for example, anabnormality detection signal (pulse) of which the level becomesinstantaneously high when an abnormality is detected, and a latchcircuit that latches the abnormality detection signal is disposedbetween the processor unit and the power module. The processor unitdetermines whether an abnormality is caused in the power module based onthe voltage level of a latch signal output from the latch circuit.

However, with the conventional configuration described above, even whenno abnormality is detected by the abnormality detection circuit, if asignal of which the level become instantaneously high is input into thelatch circuit due to, for example, the influence of noise, the voltagelevel of a latch signal output from the latch circuit may be raised tothe high level. Thus, there is a possibility that the processor unitwill execute a failsafe process such as a process of stopping a motor inspite of the fact that the power module is operating properly.

This phenomenon may occur not only in the configuration in which anabnormality detection signal output from the abnormality detectioncircuit is input into the latch circuit, but also in the configurationin which an abnormality detection signal is directly input into theprocessor unit. For example, a failsafe process may be erroneouslyexecuted when a signal having the same voltage level as that when anabnormality is detected is erroneously input into the processor unit dueto the influence of noise or the like.

SUMMARY OF THE INVENTION

One object of the invention is to provide an electric power converterconfigured to reduce the possibility that a processor unit will make anerroneous determination that an abnormality is caused in a power module.

An electric power converter according to an aspect of the inventionincludes:

a processor unit that outputs control signals; and

a power module that converts direct-current power supplied from adriving electric power source, into alternating-current power based onthe control signals.

The power module includes:

an inverter circuit in which multiple arms each having powersemiconductor devices connected in series are connected in parallel;

a driver circuit that outputs drive signals obtained by amplifying thecontrol signals based on a control voltage, to the power semiconductordevices; and

an abnormality detection circuit that executes detection of at least oneof abnormalities that are overheating of the power semiconductordevices, a short circuit in the arms, and a drop in the control voltageto be supplied to the driver circuit, and outputs an abnormalitydetection signal indicating a result of the abnormality detection to theprocessor unit.

The processor unit executes detection of a predicted state that is astage prior to occurrence of at least one of the abnormalities.

When the predicted state is not detected, the processor unit makes adetermination that the abnormality is not caused in the power module.

Before an abnormality is caused, the power module is placed in thepredicted state that is a stage prior to occurrence of an abnormality.Thus, when the predicted state is not detected, it is estimated that asignal that indicates occurrence of an abnormality and that is inputinto the processor unit is due to the influence of, for example, noise.Thus, when the predicted state is not detected, a determination that anabnormality is not caused in the power module is made. In this way, itis possible to reduce the possibility that there is an abnormality inthe power module.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further features and advantages of the invention willbecome apparent from the following description of example embodimentswith reference to the accompanying drawings, wherein like numerals areused to represent like elements and wherein:

FIG. 1 is a block diagram illustrating an electric power converter andthe configuration near the electric power converter;

FIG. 2 is a block diagram of a power module;

FIG. 3 illustrates time charts, wherein the upper half of FIG. 3illustrates time charts indicating transitions of duty command valuesand triangular waves, and the lower half of FIG. 3 illustrates timecharts indicating transitions of the on-off-states of IGBTs; and

FIG. 4 is a flowchart illustrating a procedure of abnormality detectionexecuted by a processor unit.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, an electric power converter 1 according to an embodiment ofthe invention will be described with reference to the accompanyingdrawings. The electric power converter 1 illustrated in FIG. 1 ismounted in a vehicle such as an electric vehicle or a hybrid vehicle,and converts direct-current power supplied from a driving electric powersource (driving battery) 2 into alternating-current power, and suppliesthe alternating-current power to a motor (load) 3 that serves as asource of power for propelling the vehicle. A driving electric powersource with a rated voltage of, for example, 200V is used as the drivingelectric power source 2 in the present embodiment. A brushless motorthat is operated by the received three-phase (U-phase, V-phase, W-phase)alternating-current power is adopted as the motor 3 in the presentembodiment.

As illustrated in FIG. 1, the electric power converter 1 includes aprocessor unit 11 and a power module 12. The processor unit 11 outputsmotor control signals S_mc that are control signals for controlling theoperation of the motor 3. The power module 12 converts direct-currentpower supplied from the driving electric power source 2 intoalternating-current power based on the motor control signals S_mc.

The processor unit 11 is connected to a control electric power source(control battery) 13 via an electric power supply line Lc. A controlelectric power source with a rated voltage of, for example 12V is usedas the control electric power source 13 in the present embodiment. Acontrol relay 14, which is a mechanical relay, and a regulator circuit15, which generates a constant voltage, are disposed at an intermediateportion of the electric power supply line Lc. An IG signal S_igindicating the state of an ignition switch (IG) of the vehicle is inputinto the control relay 14. When the IG signal S_ig indicating theon-state of the ignition switch is input into the control relay 14, thecontrol relay 14 is placed in the on-state. When the IG signal S_igindicating the off-state of the ignition switch is input into thecontrol relay 14, the control relay 14 is placed in the off-state. Theregulator circuit 15 generates a voltage to be supplied (applied) to theprocessor unit 11, based on an electric power supply voltage Vc suppliedfrom the control electric power source 13. The voltage to be supplied tothe processor unit 11 is, for example, 5V. When the control relay 14 isplaced in the on-state and the electric power supply line Lc is broughtinto electrical conduction, the processor unit 11 operates uponreception of a constant voltage supplied from the regulator circuit 15and the processor unit 11 outputs the motor control signals S_mc to thepower module 12 based on a vehicle signal S_car as described later.

The power module 12 includes an inverter circuit 21 including aplurality of power semiconductor devices connected to each other, and adriver circuit 22 that outputs motor drive signals (gate on-off signals)S_mp to the inverter circuit 21. The power semiconductor devices areinsulated gate bipolar transistors (IGBTs) 32 a to 32 f illustrated inFIG. 2. The driver circuit 22 amplifies the motor control signals S_mcto generate the motor drive signals S_mp, thereby driving the invertercircuit 21.

The inverter circuit 21 is connected to the driving electric powersource 2 via an electric power supply line Lp, and the driver circuit 22is connected to the control electric power source 13 via the electricpower supply line Lc. A driving relay 23, which is a mechanical relay,is disposed at an intermediate portion of the electric power supply lineLp. When the driving relay 23 is placed in the on-state and the electricpower supply line Lp is brought into electrical conduction, the invertercircuit 21 is allowed to supply the motor 3 with alternating-currentpower based on an electric power supply voltage Vp supplied from thedriving electric power source 2. A boosting circuit 24 that boosts theelectric power supply voltage Vc supplied from the control electricpower source 13 is disposed at an intermediate portion of the electricpower supply line Lc. The driver circuit 22 amplifies the motor controlsignals S_mc based on a control voltage Vcb (e.g., 15V) output from theboosting circuit 24, and outputs the amplified signals to the invertercircuit 21. As the power semiconductor devices are turned on or offbased on the motor drive signals S_mp, the inverter circuit 21 outputs,to the motor 3, alternating-current power based on the electric powersupply voltage Vp supplied from the driving electric power source 2.

The details of the power module 12 are illustrated in FIG. 2. Theinverter circuit 21 is a PWM inverter in which arms (switching arms) 31u, 31 v, 31 w are connected in parallel so as to correspond respectivelyto the three phases of the motor. Specifically, the arms 31 u, 31 v, 31w are respectively formed by connecting the IGBT 32 a and the IGBT 32 din series, connecting the IGBT 32 b and the IGBT 32 e in series, andconnecting the IGBT 32 c and the IGBT 32 f in series. Connection points33 u, 33 v, 33 w, which are respectively located between the IGBT 32 aand the IGBT 32 d, between the IGBT 32 b and the IGBT 32 e, and betweenthe IGBT 32 c and the IGBT 32 f, are connected to three-phase motorcoils 34 u, 34 v, 34 w (see FIG. 1). Each of the IGBTs 32 a to 32 f isprovided with a diode (not illustrated) that allows electricalconduction from the emitter side to the collector side.

The driver circuit 22 includes, for example, a plurality of operationalamplifiers (not illustrated) corresponding to the IGBTs 32 a to 32 f,and the motor control signals S_mc are input into the operationalamplifiers from the processor unit 11. The motor control signals S_mcare input into input terminals of the operational amplifiers viaphotocouplers (not illustrated), and the processor unit 11 and the powermodule 12 are electrically insulated from each other. The controlvoltage Vcb boosted by the boosting circuit 24 is supplied (applied) tothe driver circuit 22. The driver circuit 22 amplifies the receivedmotor control signals S_mc based on the supplied control voltage Vcb,thereby outputting the motor drive signals S_mp to the gate terminals ofthe IGBTs 32 a to 32 f. Thus, in the inverter circuit 21, the IGBTs 32 ato 32 f are turned on or off in response to the three-phase motor drivesignals S_mp, and the patterns of electrical conduction to thethree-phase motor coils 34 u, 34 v, 34 w are switched. As a result,three-phase alternating-current power is supplied to the motor 3.

As illustrated in FIG. 1, the processor unit 11 receives the vehiclesignal S_car indicating, for example, an accelerator pedal depressionamount that indicates a depressed amount of an accelerator pedal (notillustrated) of the vehicle or a vehicle speed. The processor unit 11computes a target torque for the motor 3 based on the vehicle signalS_car, and outputs the motor control signals S_mc for controlling themotor 3 such that the target torque is generated. The processor unit 11in the present embodiment receives three-phase currents Iu, Iv, Iw forthe motor 3, which are detected by three-phase current sensors 35 u, 35v, 35 w, and a rotation angle θ of the motor 3, which is detected by aresolver 36. The processor unit 11 executes current feedback controlsuch that the three-phase currents Iu, Iv, Iw follow three-phase currentcommand values corresponding to the torque to be generated by the motor3, thereby outputting the motor control signals S_mc.

Each motor control signal S_mc in the present embodiment is a pulsesignal subject to pulse width modulation (PWM) control. Specifically, asillustrated in FIG. 3, the processor unit 11 generates the motor controlsignals S_mc to be output to the power module 12, based on thecomparison between three-phase duty command values Du, Dv, Dwcorresponding to the three-phase current command values computed throughexecution of the current feedback control and triangular waves that arePWM carriers (carrier waves). The processor unit 11 uses two triangularwaves δ1, δ2 shifted from each other in the up-down direction in FIG. 3and having the same phase (the duty ratio based on the triangular waveδ1>the duty ratio based on the triangular wave δ2), and thus sets deadtimes td during which the IGBTs 32 a to 32 c on the high potential side(upper side) in the arms 31 u, 31 v, 31 w and the IGBTs 32 d to 32 f onthe low potential side (lower side) in the arms 31 u, 31 v, 31 w areboth maintained in the off-state. Specifically, in each dead time td,the IGBTs 32 a, 32 d of the arm 31 u, or the IGBTs 32 b, 32 e of the arm31 v, or the IGBTs 32 c, 32 f of the arm 31 w are respectivelymaintained in the off-state.

Specifically, the processor unit 11 generates the motor control signalsS_mc such that, when each of the three-phase duty command values Du, Dv,Dw is higher than the value of the triangular wave δ1, which is setabove the triangular wave δ2 in FIG. 3, a corresponding one of thethree-phase upper IGBTs 32 a to 32 c is maintained in the on-state,whereas when each of the three-phase duty command values Du, Dv, Dw islower than the value of the triangular wave δ1, a corresponding one ofthe three-phase upper IGBTs 32 a to 32 c is maintained in the off-state.Similarly, the processor unit 11 generates the motor control signalsS_mc such that, when each of the three-phase duty command values Du, Dv,Dw is lower than the value of the triangular wave δ2, which is set belowthe triangular wave δ1 in FIG. 3, a corresponding one of the three-phaselower IGBTs 32 d to 32 f is maintained in the on-state, whereas wheneach of the three-phase duty command values Du, Dv, Dw is higher thanthe value of the triangular wave δ2, a corresponding one of thethree-phase lower IGBTs 32 d to 32 f is maintained in the off-state.

As illustrated in FIG. 1, the IG signal S_ig is input into the processorunit 11. When the processor unit 11 receives the IG signal S_igindicating the on-state of the ignition switch, the processor unit 11outputs the relay control signal S_rl for placing the driving relay 23in the on-state. When the processor unit 11 receives the IG signal S_igindicating the off-state of the ignition switch, the processor unit 11outputs the relay control signal S_rl for placing the driving relay 23in the off-state.

As illustrated in FIG. 2, the power module 12 is configured as aso-called intelligent power module (IPM) that detects abnormalities suchas overheating of the IGBTs 32 a to 32 f, a short circuit in the arms 31u, 31 v, 31 w, and a drop in the control voltage Vcb. A latch circuit 41that latches (holds a state of) an abnormality detection signal S_eroutput from the power module 12 is disposed between the processor unit11 and the power module 12. The processor unit 11 determines whether anabnormality is caused in the power module 12 based on the voltage levelof a latch signal S_lat. When it is determined that an abnormality iscaused, the processor unit 11 executes a failsafe process of stoppingthe motor 3 by stopping the power module 12.

Specifically, the power module 12 includes an overheating detectioncircuit 42 that detects overheating of the IGBTs 32 a to 32 f, ashort-circuit detection circuit 43 that detects a short circuit in thearms 31 u, 31 v, 31 w, and a voltage drop detection circuit 44 thatdetects a drop in the control voltage Vcb. That is, in the presentembodiment, each of the overheating detection circuit 42, theshort-circuit detection circuit 43 and the voltage drop detectioncircuit 44 may function as an abnormality detection circuit.

A temperature sensor 45 disposed near the IGBT 32 e is connected to theoverheating detection circuit 42. The overheating detection circuit 42executes a comparison in magnitude between a detected temperature Tdetected by the temperature sensor 45 and a temperature abnormalitydetermination threshold Tth_er that is set in advance. When the detectedtemperature T is equal to or lower than the temperature abnormalitydetermination threshold Tth_er, the overheating detection circuit 42determines that the IGBTs 32 a to 32 f are not overheated, and outputs alow-level abnormality detection signal S_er. On the other hand, when thedetected temperature T is higher than the temperature abnormalitydetermination threshold Tth_er, the overheating detection circuitdetermines that the IGBTs 32 a to 32 f are overheated, and outputs anabnormality detection signal S_er of which the level becomesinstantaneously high, that is, a pulse signal.

Voltage sensors 46 a to 46 f that respectively detect inter-terminalvoltages Va to Vf between collector terminals and emitter terminals ofthe three-phase IGBTs 32 a to 32 f are connected to the short-circuitdetection circuit 43. The short-circuit detection circuit 43 executes acomparison in magnitude between (the absolute values of) theinter-terminal voltages Va to Vf detected by the voltage sensors 46 a to46 f and an inter-terminal voltage abnormality determination thresholdVxth_er. The inter-terminal voltage abnormality determination thresholdVxth_er is a voltage that is generated between the collector terminaland the emitter terminal when each of the IGBTs 32 a to 32 f is stuck inthe on-state due to a malfunction, and is obtained by, for example, anexperiment in advance. When each of all the inter-terminal voltages Vato Vf is equal to or lower than the inter-terminal voltage abnormalitydetermination threshold Vxth_er, the short-circuit detection circuit 43determines that no short circuit occurs in the arms 31 u, 31 v, 31 w,and outputs a low-level abnormality detection signal S_er. On the otherhand, when at least one of the inter-terminal voltages Va to Vf ishigher than the inter-terminal voltage abnormality determinationthreshold Vxth_er, the short-circuit detection circuit 43 determinesthat a short circuit occurs in the arms 31 u, 31 v, 31 w, and outputs apulsed abnormality detection signal S_er of which the level becomesinstantaneously high.

A voltage sensor 47 that detects the control voltage Vcb to be suppliedto the driver circuit 22 is connected to the voltage drop detectioncircuit 44. The voltage drop detection circuit 44 executes a comparisonin magnitude between the absolute value of the control voltage Vcbdetected by the voltage sensor 47 and a control voltage abnormalitydetermination threshold Vcbth_er that is set in advance. When thecontrol voltage Vcb is higher than the control voltage abnormalitydetermination threshold Vcbth_er, the voltage drop detection circuit 44determines that there is no drop in the control voltage Vcb, and outputsa low-level abnormality detection signal S_er. On the other hand, whenthe control voltage Vcb is equal to or lower than the control voltageabnormality determination threshold Vcbth_er, the voltage drop detectioncircuit 44 determines that the control voltage Vcb drops, and outputs apulsed abnormality detection signal S_er of which the level becomesinstantaneously high.

When the latch circuit 41 receives a pulsed abnormality detection signalS_er of which the level becomes instantaneously high from at least oneof the overheating detection circuit 42, the short-circuit detectioncircuit 43 and the voltage drop detection circuit 44, the latch circuit41 switches the voltage level of the latch signal S_lat from the lowlevel to the high level and maintains the voltage level of the latchsignal S_lat at the high level. When the processor unit 11 receives ahigh-level latch signal S_lat from the latch circuit 41, the processorunit 11 executes a shutdown process of, for example, outputting a relaycontrol signal S_rl for placing the driving relay 23 in the off-state,or stopping output of the motor control signals S_mc, and thus stops themotor 3 by stopping the power module 12.

Even when none of the short-circuit detection circuit 43, theoverheating detection circuit 42 and the voltage drop detection circuit44 detects an abnormality, if a signal of which the level becomeinstantaneously high is input into the latch circuit 41 due to, forexample, the influence of noise, the voltage level of the latch signalS_lat may be raised to the high level.

On the basis of this fact, the processor unit 11 executes detection ofan overheating predicted state that is a stage prior to overheating ofthe IGBTs 32 a to 32 f, a short circuit predicted state that is a stageprior to a short circuit in the arms 31 u, 31 v, 31 w, and a voltagedrop predicted state that is a stage prior to a drop in the controlvoltage Vcb. When none of these predicted states is detected, adetermination that an abnormality is caused is not made even if thevoltage level of the latch signal S_lat is switched to the high level.When the overheating predicted state is detected, the processor unit 11makes the duty ratio of each motor control signal S_mc lower than thatwhen the overheating predicted state is not detected. When theshort-circuit predicted state is detected, the processor unit 11 makesthe dead time td longer than that when the short-circuit predicted stateis not detected. When the voltage drop predicted state is detected, theprocessor unit 11 stops the power module 12 by executing the shutdownprocess.

Specifically, the temperature sensor 45 is connected to the processorunit 11. The processor unit 11 executes detection of the overheatingpredicted state based on a comparison in magnitude between the detectedtemperature T detected by the temperature sensor 45 and a temperatureprediction value Tth_pr. The temperature prediction value Tth_pr is setto a value lower than the temperature abnormality determinationthreshold Tth_er. When the detected temperature T is higher than thetemperature prediction value Tth_pr, the processor unit 11 determinesthat the power module 12 is in the overheating predicted state. When theoverheating predicted state is detected, the processor unit 11 sets anupper limit that is smaller than 100%, for the duty command values Du,Dv, Dw, and thus imposes a limitation so that the duty ratio of eachmotor control signal S_mc is lowered. That is, when the three-phase dutycommand values Du, Dv, Dw exceed the upper limit, the processor unit 11outputs such motor control signals S_mc that the IGBTs 32 a to 32 f areturned on and off based on the duty ratio indicated by the upper limit.

In addition, a voltage sensor 48 that detects the electric power supplyvoltage Vp supplied from the driving electric power source 2 and acurrent sensor 49 that detects a driving current I flowing through theinverter circuit 21 (electric current to be applied to the motor 3) areconnected to the processor unit 11. The processor unit 11 executesdetection of the short-circuit predicted state based on a comparison inmagnitude between (the absolute value of) the electric power supplyvoltage Vp supplied from the driving electric power source 2, which isdetected by the voltage sensor 48, and an electric power supply voltageprediction value Vpth_pr, and based on a comparison in magnitude between(the absolute value of) the driving current I, which is detected by thecurrent sensor 49, and a driving current prediction value Ith_pr. Theelectric power supply voltage prediction value Vpth_pr is set to a valuelower than an electric power supply voltage abnormality determinationthreshold Vpth_er indicating that a short circuit occurs in any one ofthe arms 31 u, 31 v, 31 w. The driving current prediction value Ith_pris set to a value lower than a driving current abnormality determinationthreshold Ith_er indicating that a short circuit occurs in any one ofthe arms 31 u, 31 v, 31 w. When the electric power supply voltage Vpsupplied from the driving electric power source 2 is equal to or lowerthan the electric power supply voltage prediction value Vpth_pr and thedriving current I is higher than the driving current prediction valueIth_pr, the processor unit 11 determines that the power module 12 is inthe short-circuit predicted state. When the short-circuit predictedstate is detected, the processor unit 11 increases the differencebetween the triangular wave δ1 and the triangular wave δ2, and thusmakes the dead time td longer.

The voltage sensor 47 that detects the above control voltage Vcb isconnected to the processor unit 11. The processor unit 11 executes acomparison in magnitude between the control voltage Vcb and a controlvoltage prediction value Vcbth_pr. The control voltage prediction valueVcbth_pr is set to a value that is higher than the control voltageabnormality determination threshold Vcbth_er. When the control voltageVcb is equal to or lower than the control voltage prediction valueVcbth_pr, the processor unit 11 determines that the power module 12 isin the voltage drop predicted state. When the voltage drop predictedstate is detected, the processor unit 11 stops the power module 12 byexecuting the shutdown process, and thus stops the motor 3.

When none of these predicted states is detected, even if a high-levellatch signal S_lat is input into the latch circuit 41, the processorunit 11 invalidates the high-level latch signal S_lat and does not stopthe motor 3. Further, the processor unit 11 in the present embodimentreturns the voltage level of the latch signal S_lat, which is outputfrom the latch circuit 41, to the low level. On the other hand, theprocessor unit 11 validates a high-level latch signal S_lat, which isinput into the latch circuit 41 after the overheating predicted state orthe short-circuit predicted state is detected, and stops the motor 3.

Next, a procedure of abnormality detection executed by the processorunit 11 in the present embodiment will be described. As illustrated in aflowchart in FIG. 4, the processor unit 11 first determines whether thelatch signal S_lat is at the high level or not (step 101). When thelatch signal S_lat is at the low level (step 101: NO), the processorunit 11 determines whether the detected temperature T is higher than thetemperature prediction value Tth_pr (step 102). When the detectedtemperature T is higher than the temperature prediction value Tth_pr(step 102: YES), the processor unit 11 determines that the power module12 is in the overheating predicted state, and imposes a limitation sothat the duty ratio of each motor control signal S_mc is lowered (step103). Then, the processor unit 11 sets a prediction flag indicating thatthe power module 12 is in the overheating predicted state or theshort-circuit predicted state (step 104), and proceeds on to step 101 todetermine whether the latch signal S_lat is at the high level.

When the detected temperature T is equal to or lower than thetemperature prediction value Tth_pr (step 102: NO), the processor unit11 determines whether the driving current I is higher than the drivingcurrent prediction value Ith_pr (step 105). When the driving current Iis higher than the driving current prediction value Ith_pr (step 105:YES), the processor unit 11 determines whether the electric power supplyvoltage Vp supplied from the driving electric power source 2 is equal toor lower than the electric power supply voltage prediction value Vpth_pr(step 106). When the electric power supply voltage Vp supplied from thedriving electric power source 2 is equal to or lower than the electricpower supply voltage prediction value Vpth_pr (step 106: YES), theprocessor unit 11 prolongs each of the dead times td, during which theIGBTs 32 a to 32 c on the high potential side (upper side) and the IGBTs32 d to 32 f on the low potential side (lower side) are both maintainedin the off-state (step 107). Then, the processor unit 11 proceeds on tostep 104 to set the prediction flag, and the proceeds on to step 101 todetermine whether the latch signal S_lat is at the high level.

When the driving current I is equal to or lower than the driving currentprediction value Ith_pr (step 105: NO), or the electric power supplyvoltage Vp supplied from the driving electric power source 2 is higherthan the electric power supply voltage prediction value Vpth_pr (step106: NO), the processor unit 11 determines whether the control voltageVcb to be supplied to the driver circuit 22 is equal to or lower thanthe control voltage prediction value Vcbth_pr (step 108). When thecontrol voltage Vcb is equal to or lower than the control voltageprediction value Vcbth_pr (step 108: YES), the processor unit 11determines that the power module 12 is in the voltage drop predictedstate, and stops the power module 12 by executing the shutdown process,and thus stops the motor 3 (step 109). When the control voltage Vcb ishigher than the control voltage prediction value Vcbth_pr (step 108:NO), the processor unit 11 determines that none of the predicted statesoccurs, and proceeds on to step 101 without setting the prediction flag,to determine whether the latch signal S_lat is at the high level.

On the other hand, when the latch signal S_lat is at the high level(step 101: YES), the processor unit 11 determines whether the predictionflag is set or not (step 110). When the prediction flag is set (step110: YES), the processor unit 11 proceeds on to step 109 to stop themotor 3. On the other hand, when the prediction flag is not set (step110: NO), the processor unit 11 determines that the voltage level of thelatch signal S_lat is raised to the high level due to, for example, theinfluence of noise, and invalidates the latch signal S_lat and returnsthe voltage level of the latch signal S_lat to the low level (step 111).Then, the processor unit 11 proceeds on to step 101 to determine whetherthe latch signal S_lat is at the high level.

Next, the operations of the present embodiment will be described. Whennone of the overheating predicted state, the short-circuit predictedstate and the voltage drop predicted state is detected, it is estimatedthat a high-level latch signal S_lat input into the processor unit 11 isdue to, for example, the influence of noise, and thus the processor unit11 makes a determination that an abnormality is not caused in the powermodule 12. Therefore, even when the voltage level of the latch signalS_lat erroneously becomes the high level due to, for example, theinfluence of noise, the motor 3 is not stopped and the vehicle is ableto continue to travel using the motor 3. When the overheating predictedstate is detected by the processor unit 11, the duty ratio of each motorcontrol signal S_mc is limited. Thus, the time during which each of theIGBTs 32 a to 32 f is maintained in the on-state, that is, the timeduring which electric current is applied to each of the IGBTs 32 a to 32f is shortened, and heating thereof is suppressed. When the shortcircuit predicted state of the arms 31 u, 31 v, 31 w is detected by theprocessor unit 11, the dead time td is prolonged, and thus aninstantaneous short circuit caused by a time delay of switchover betweenthe on-state and the off-state of the IGBTs 32 a to 32 f is less likelyto occur.

Next, the advantageous effects of the present embodiment will bedescribed.

1) The processor unit 11 executes detection of the overheating predictedstate, the short-circuit predicted state and the voltage drop predictedstate. When none of these predicted states is detected, the processorunit 11 makes a determination that an abnormality is not caused in thepower module 12. Thus, it is possible to reduce the possibility that anerroneous determination that an abnormality is caused in the powermodule 12 will be made.

2) When the overheating predicted state is detected, the processor unit11 limits the upper limit of the duty ratio of each motor control signalS_mc. Thus, it is possible to suppress heating of the IGBTs 32 a to 32f. As a result, it is possible to avoid the occurrence of a situationwhere overheating of the inverter circuit 21 is detected by theoverheating detection circuit 42 and thus the motor 3 is required to bestopped.

3) When the short circuit predicted state of the arms 31 u, 31 v, 31 wis detected, the processor unit 11 prolongs the dead time td, and thusan instantaneous short circuit caused by a time delay of switchoverbetween the on-state and the off-state of the IGBTs 32 a to 32 f is lesslikely to occur. As a result, it is possible to avoid the occurrence ofa situation where a short circuit in the arms 31 u, 31 v, 31 w isdetected by the short-circuit detection circuit 43 and thus the motor 3is required to be stopped.

4) When the voltage drop predicted state of the control voltage Vcb isdetected, the processor unit 11 stops the power module 12. Thus, afailsafe process is promptly executed before the possibility that theinverter circuit 21 will fail to properly operate due to a drop in thecontrol voltage Vcb is raised.

The above-described embodiment may be modified as follows. In theabove-described embodiment, as the control voltage Vcb supplied to thedriver circuit 22, the control voltage Vcb obtained by boosting theelectric power supply voltage Vc supplied from the control electricpower source 13 using the boosting circuit 24 is supplied to the drivercircuit 22. However, for example, the electric power supply voltage Vcsupplied from the control electric power source 13 may be supplied tothe driver circuit 22 as it is.

In the above-described embodiment, the short-circuit detection circuit43 executes detection of a short circuit in the arms 31 u, 31 v, 31 wbased on a comparison in magnitude between each of the inter-terminalvoltages Va to Vf and the inter-terminal voltage abnormalitydetermination threshold Vxth_er. However, the short-circuit detectioncircuit 43 executes detection of a short circuit in the arms 31 u, 31 v,31 w based on a comparison in magnitude between, for example, thedriving current I flowing through the inverter circuit 21 and thedriving current abnormality determination threshold Ith_er.

In the above-described embodiment, the overheating predicted state isdetected based on the detected temperature T detected by the temperaturesensor 45 of the power module 12. However, a temperature sensordifferent from the temperature sensor 45 of the power module 12 may beprovided to detect the overheating predicted state based on thetemperature detected by this temperature sensor. Similarly, a voltagesensor that differs from the voltage sensor 47 of the power module 12and that detects the control voltage Vcb may be provided to detect thevoltage drop predicted state based on the control voltage detected bythis voltage sensor.

In the above-described embodiment, the short-circuit predicted state isdetected based on the driving current I detected by the current sensor49. However, the driving current may be estimated based on, for example,the three-phase currents Iu, Iv, Iw respectively detected by the phasecurrent sensors 35 u, 35 v, 35 w, and the short-circuit predicted statemay be detected based on the estimated values.

In the above-described embodiment, when both a) the condition that theelectric power supply voltage Vp supplied from the driving electricpower source 2 is higher than the electric power supply voltageprediction value Vpth_pr, and b) the condition that the driving currentI is higher than the driving current prediction value Ith_pr aresatisfied, it is determined that the power module 12 is in theshort-circuit predicted state. However, when one of the condition a) andthe condition b) is satisfied, it may be determined that the powermodule 12 is in the short-circuit predicted state.

In the above-described embodiment, the short-circuit predicted state maybe detected based on only a comparison in magnitude between the electricpower supply voltage Vp supplied from the driving electric power source2 detected by the voltage sensor 48 and the electric power supplyvoltage prediction value Vpth_pr, or only a comparison in magnitudebetween the driving current I detected by the current sensor 49 and thedriving current prediction value Ith_pr.

In the above-described embodiment, detection of the overheatingpredicted state, detection of the short-circuit predicted state, anddetection of the voltage drop predicted state are executed in the statedorder. However, the order of executing these detection may be changed asneeded. In the above-described embodiment, when the overheatingpredicted state is detected, the upper limit of the duty ratio of eachmotor control signal S_mc is limited to make the duty ratio of the motorcontrol signal S_mc lower than that in the normal state. However, forexample, each of the computed duty command values Du, Dv, Dw may bemultiplied by a coefficient that is equal to or larger than zero andsmaller than one to make the duty ratio of each motor control signalS_mc lower than that in the normal state.

In the above-described embodiment, even when the overheating predictedstate is detected, the duty ratio of the motor control signal S_mc neednot be made lower than that in the normal state. In the above-describedembodiment, even when the short circuit predicted state of the arms 31u, 31 v, 31 w is detected, the dead time td need not be prolonged.

In the above-described embodiment, when the voltage drop predicted stateis detected, instead of a failsafe process of stopping the power module12 to stop the motor 3, another process may be executed.

In the above-described embodiment, the power module 12 executesdetections of three kinds of abnormalities, that is, overheating of theIGBTs 32 a to 32 f, a short circuit in the arms 31 u, 31 v, 31 w, and avoltage drop of the control electric power source 13. However, the powermodule 12 may execute detection of at least one of the three kinds ofabnormalities. For example, overheating of the IGBTs 32 a to 32 f neednot be detected. In this case, the processor unit 11 detects only apredicted state corresponding to the abnormality detection executed bythe power module 12.

In the above-described embodiment, the abnormality detection signal S_eroutput from the power module 12 is input into the processor unit 11 viathe latch circuit 41. However, the abnormality detection signal S_er maybe input directly into the processor unit 11.

In the above-described embodiment, the inverter circuit 21 is formed ofthe IGBTs 32 a to 32 f. However, the inverter circuit 21 may be formedof, for example, other power semiconductor devices such as field effecttransistors (FETs).

In the above-described embodiment, the electric power converter 1supplies alternating-current power to the motor 3 for propelling thevehicle, which is mounted in the vehicle. However, the electric powerconverter 1 may supply alternating-current power to a motor for otheruses or a load other than a motor.

What is claimed is:
 1. An electric power converter comprising: a processor unit that outputs control signals; and a power module that converts direct-current power supplied from a driving electric power source, into alternating-current power based on the control signals, the power module including an inverter circuit in which multiple arms each having power semiconductor devices connected in series are connected in parallel, a driver circuit that outputs drive signals obtained by amplifying the control signals based on a control voltage, to the power semiconductor devices, and an abnormality detection circuit that executes detection of at least one of abnormalities that are overheating of the power semiconductor devices, a short circuit in the arms, and a drop in the control voltage to be supplied to the driver circuit, and outputs an abnormality detection signal indicating a result of the abnormality detection to the processor unit, wherein the processor unit executes detection of a predicted state that is a stage prior to occurrence of at least one of the abnormalities, and when the predicted state is not detected, the processor unit makes a determination that the abnormality is not caused in the power module.
 2. The electric power converter according to claim 1, wherein when a predicted state of overheating of the power semiconductor devices is detected, the processor unit makes a duty ratio of each of the control signals lower than that when the predicted state of overheating of the power semiconductor devices is not detected.
 3. The electric power converter according to claim 1, wherein when a predicted state of a short circuit in the arms is detected, the processor unit makes a dead time during which both the power semiconductor device on a high potential side and the power semiconductor device on a low potential side are maintained in an off-state, longer than that when the predicted state of a short circuit in the arms is not detected.
 4. The electric power converter according to claim 2, wherein when a predicted state of a short circuit in the arms is detected, the processor unit makes a dead time during which both the power semiconductor device on a high potential side and the power semiconductor device on a low potential side are maintained in an off-state, longer than that when the predicted state of a short circuit in the arms is not detected.
 5. The electric power converter according to claim 1, wherein when a predicted state of a drop in the control voltage is detected, the processor unit stops the power module.
 6. The electric power converter according to claim 1, wherein: the abnormality detection circuit executes detection of overheating of the power semiconductor devices based on a comparison in magnitude between each of detected temperatures of the power semiconductor devices detected by a temperature sensor and a temperature abnormality determination threshold; and the processor unit executes detection of a predicted state of overheating of the power semiconductor devices based on a comparison in magnitude between each of the detected temperatures and a temperature prediction value indicating a temperature lower than the temperature abnormality determination threshold.
 7. The electric power converter according to claim 1, wherein: the abnormality detection circuit executes detection of a short circuit in the arms based on a comparison in magnitude between an inter-terminal voltage of each of the power semiconductor devices and an inter-terminal voltage abnormality determination threshold; and the processor unit executes detection of a predicted state of a short circuit in the arms based on a comparison in magnitude between an electric power supply voltage supplied from the driving electric power source and an electric power supply voltage prediction value that is lower than an electric power supply voltage abnormality determination threshold indicating that a short circuit occurs in the arms.
 8. The electric power converter according to claim 1, wherein: the abnormality detection circuit executes detection of a short circuit in the arms based on a comparison in magnitude between an inter-terminal voltage of each of the power semiconductor devices and an inter-terminal voltage abnormality determination threshold; and the processor unit executes detection of a predicted state of a short circuit in the arms based on a comparison in magnitude between a driving current flowing through the inverter circuit and a driving current prediction value that is lower than a driving current abnormality determination threshold indicating that a short circuit occurs in the arms.
 9. The electric power converter according to claim 7, wherein: the abnormality detection circuit executes detection of a short circuit in the arms based on a comparison in magnitude between an inter-terminal voltage of each of the power semiconductor devices and an inter-terminal voltage abnormality determination threshold; and the processor unit executes detection of a predicted state of a short circuit in the arms based on a comparison in magnitude between a driving current flowing through the inverter circuit and a driving current prediction value that is lower than a driving current abnormality determination threshold indicating that a short circuit occurs in the arms.
 10. The electric power converter according to claim 1, wherein: the abnormality detection circuit executes detection of a drop in the control voltage based on a comparison in magnitude between the control voltage to be supplied to the driver circuit and a control voltage abnormality determination threshold; and the processor unit executes detection of a predicted state of a drop in the control voltage based on a comparison in magnitude between the control voltage to be supplied to the driver circuit and a control voltage prediction value that is lower than the control voltage abnormality determination threshold. 